A passive optical network (PON) consists of one or more Optical Line Termination (OLT) systems, a number of Optical Network Units (ONUs), and an optical distribution network (ODN) including fibers and splitters between the OLT systems and the ONUs. Each OLT system is a service provider node located in a central office, and each ONU is a subscriber node. One type of PON is a wavelength division multiplexing (WDM) PON, which multiplexes a number of optical carrier signals onto a single optical trunk fiber by using different wavelengths (colors) of laser light. The wavelengths are arranged to serve disjoint subsets of the ONUs.
One conventional method for protecting network and equipment in a PON uses a protection port for every working port. Such protection method is described in, for example, ITU-T G.984.1. The need to dedicate a protection facility to each working facility, along with its port electronics and a significant share of the electronics beyond the port, adds substantial cost to the network. The cost of this mostly unused protection facility and its electronics may exceed the value of protection, leading to the omission of protection and hence, lower service reliability.